Fluorescence will be used to characterize the interaction of the ionophore A23187 with phospholipid bilayers. Partitioning of the ionophore into vesicles will be quantitated through detection of fluorescence enhancement. Employing lipid spin labels as quenchers of the fluorescence, distribution of ionophore across the bilayer will be probed. Effects of lipid fluidity on the partitioning will be investigated. Electron paramagnetic resonance (EPR) will be used to characterize the interaction of divalent cations with biological and model membranes. For this work Mn2 ion is used as a paramagnetic Ca2 ion/Mg2 ion analog. One aim will be to establish methodology for distingishing spectrally between Mn2 plus ions held in a diffuse double layer and those complexed to a surface. Techniques for assaying membrane fusion will be developed which are based on mixing of trapped contents of two liposomes. The influence of various parameters on fusion will be investigated. These include: lipid head group (charge), fluidity, divalent cations, etc.